It means shale gas firms operating in the UK may face a greater regulatory burden than conventional onshore oil and gas operations.

"There is a distinction between reinjection for conventional oil and gas activities, such as at Wytch Farm, and reinjection from unconventional activities, such as from shale gas operations," said the Environment Agency.

"For conventional activities, we would allow operators to reinject produced water into the formation from which it was generated to facilitate production."

"For shale gas operations, the disposal method for flow-back fluid will be agreed between the operator, their contractors and us."

Options could include on-site treatment or disposal at a waste treatment facility - but not re-injection.

The move appears designed to limit the risk of earthquakes from shale gas operations which has been a source of considerable controversy.

Reinjection and the risk of earthquakes

The Glasgow study by Dr Rob Westaway and Prof Paul Younger was published in the peer reviewed Quarterly Journal of Engineering Geology and Hydrogeology.

Its findings appear to contradict earlier studies - including a Royal Society report - that suggested that even small tremors may pose a risk to well integrity.

It found the size of an earthquake caused by fracking was limited by the length of the fracture.

Because fractures cannot exceed 600 metres the most significant earthquake fracking could plausibly cause would be around 3.6 on the Richter scale.

This - they said - would be more significant than their proposed new threshold and could cause minor damage “such as cracks to plaster”.

Their analysis of the size and probability of earthquakes in the UK is based on an assumption that regulators will not allow firms to re-inject water which comes back to the surface.

Fracking involves the use of large volumes of water mixed with chemicals to open up the rock much of which returns to the surface and must be safely disposed of.

“By far the biggest cause of serious seismic incidents isn’t the drilling or the fracking process itself. Instead, it’s the practice of disposing of waste water back into the borehole once the process is finished,” said Younger.

A recent study published in the journal Science and reported inScientific American found a strong link between the injection of wastewater and significant earthquakes.

Re-injection, however, does take place in the UK already - for conventional oil and gas drilling and had been considered as an option for fracking.

One of the difficulties in handling flow-back fluid from fracking (and other oil drilling operations) is that it contains low levels of Naturally Occurring Radioactive Waste (NORM) picked up from the rocks (see our explainer here).

In January this year a Scottish government consultation noted:

“Wytch Farm in Dorset generates the most produced water… Produced water is disposed of at Wytch Farm by re-injection; this is permitted by the Environment Agency,” indeed - this is no secret, it’s in The Telegraph and was confirmed to us by sources in the industry.

But what about other sites? Well, a guidance note for the Environment Agency’s regulation of shale gas observed that:

“Treatment and disposal may take place on-site leading to re-injection during subsequent hydraulic fracturing”

However the latest statement appears to contradict this.

Small earthquakes and well integrity

One of the key arguments made in the Glasgow study is that seismic events 2.5 kilometres below ground have little, if any, perceptible impact on the surface.

That’s why the authors recommended adopting the same kind of regulation as currently applies to quarry blasting, limiting peak ground velocities to different levels depending on the time of day to levels that are “similar in magnitude to nuisance activities such as walking on wooden floors”

The levels they recommend, they suggest, would add up to a tremor 2.5km below ground of around 3 on the Richter scale - far far higher than the government’s 0.5.

However in its study on shale gas regulation the Royal Society notes “discussions about the magnitude of seismicity induced by hydraulic fracturing often focus on the limited (if any) damage at the surface.”

Instead, the Royal Society argue, “Attention should also be given to any damage to well integrity. Tests carried out after Cuadrilla’s second fracturing stage and 2.3 ML seismic event revealed deformation of the Preese Hall well casing.”

That deformation, from a small quake, didn’t actually compromise the well. Indeed it is hard to know if wells would be compromised by tremors, however - to check - the Royal Society say that following tremors checks should be made reviewed by an independent examiner.

In its recommendations the Royal Society suggests a Traffic Light monitoring system whereby extra monitoring measures would be implemented after small tremors (below 1.7) for two days or until seismicity has reduced significantly and drilling would be stopped entirely above 1.7.

The report notes that the thresholds could be ground - rather than seismicity - based, but the monitoring still needs to include below ground seismicity.

A DECC report into Cuadrilla’s Lancashire quakes opted for a more conservative threshold of 0.5 but also noted that no quake should be allowed above 2.6 - the German standard for damage to property.

Of course monitoring of small quakes becomes more important if there is a genuine risk of larger ones and that, in turn, depends on whether you fear induced seismicity as a result of wastewater injection.

The Royal Society advises that key to mitigating the risk of tremors from injecting wastewater is to “be prepared to alter plans”, perhaps this is what the government's environmental regulators have just done.

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